The present invention relates to an electropneumatic brake control system for a railway train in which the train brake pipe pressure can be recharged without concurrently effecting a release of the train brakes.
A brake equipment of the foregoing type employs trainline wires via which an application magnet valve and a holding magnet valve on each car is controlled. The application magnet valve effects a reduction of brake pipe pressure electrically in response to which the car control valve operates to supply air to the car brake cylinders, when a brake application is initiated through the locomotive brake valve. When it is desired to recharge the train brake pipe without concurrently releasing the car brakes, the locomotive brake valve is set in holding position, wherein the car holding magnet valve interrupts the exhaust of brake cylinder pressure via the car control valve until such time as the brake valve is moved to release position, it being understood that the brake valve in holding position establishes recharging of the train brake pipe the same as in release position. Typically, a standard 26-E type brake valve having electrical contacts controlled by movement of the brake valve handle has been employed to control the trainline wires through which the foregoing application and holding magnet valves are operated.
The recently introduced 30-type brake valve has been designed for desk-style mounting to meet the desire to modernize locomotive cab designs, as opposed to the pedestal-style 26-type brake valves. In developing a 30-type brake valve capable of operating trainline wires in the manner of the aforementioned 26-E brake valve, one such design employs pressure-actuated electrical switches that are operable in response to the different handle positions of the brake valve, as opposed to handle-operated electrical contacts. One such pressure switch is controlled in accordance with the pressure state of a pneumatic signal that transitions between release and holding positions of the brake valve.
This pneumatic signal also controls a release control valve of the standard P-2-A brake application valve. When employed with safety monitoring devices such as periodically require the operator to indicate his alertness and well-being, for example, the P-2-A brake application valve enforces an automatic penalty brake application in the event such periodic acknowledgment is not forthcoming. This is accomplished by venting equalizing reservoir pressure which, in turn, causes the brake valve relay valve portion to vent brake pipe pressure in a well-known manner and thereby force the car control valve to effect an automatic brake application in circumvention of the operator's control, i. e., with the brake valve handle set in release position.
The pressure state of the aforementioned pneumatic signal, that controls both the holding magnet valve and the release control valve of the P-2-A brake application valve, transitions when the brake valve handle is moved out of release position, as required to reset the P-2-A brake application valve. This pressure transition of the pneumatic signal conditions the release control valve of the P-2-A brake application valve to cut off communication between the equalizing reservoir and its charging source while equalizing reservoir pressure is vented via the main spool of the P-2-A brake application valve. If it is desired to recharge the brake pipe without releasing the brake application in electropneumatic mode of operation, by moving the brake valve handle to holding position, the pneumatic signal controlling both the holding magnet valve as well as the release control valve of the P-2-A brake application valve does not transition back to the pressure state condition it normally assumes in release position. Consequently, no pressure signal is available to reset the release control valve from its actuated position to which it is operated by "lockover" port pressure during reset of the P-2-A brake application valve main spool.
Since the release control valve in its actuated position cuts off the recharging of equalizing reservoir pressure, the brake valve relay valve portion, which responds to the equalizing reservoir/brake pipe pressure differential, is in effect rendered inoperative to recharge the brake pipe pressure. Thus, the brake valve handle must be moved to release position in order to obtain a pressure signal to reset the release control valve and thereby permit the equalizing reservoir pressure and thus the brake pipe pressure to be recharged. However, since this effects a brake release, it will be appreciated that the advantage of a brake valve device and appropriately designed equipment to permit recharging the brake pipe pressure without concurrently releasing the train brakes in holding position of the brake valve is not realized.